Polystyrene recycling process

ABSTRACT

The invention comprises a method and apparatus for recycling foamed polystyrene from municipal solid waste and more particularly, from fast food restaurant waste. A steady stream of waste is delivered to a flail mill for reducing particle size, a rotary trommel for eliminating undersized waste and a rotary air classifier for removing &#34;heavy&#34; waste from the stream. At this point, the waste stream comprises mostly paper and foamed polystyrene. The paper and foamed polystyrene are delivered to a water pulper which fiberizes the paper so that it can then be separated from the foamed polystyrene by passing it through a screen of selected mesh size to allow the water and paper pulp to pass through while retaining the foamed polystyrene.

This application is a continuation of application Ser. No. 07/376,746,filed July 7, 1989, now abandoned.

1. Field of the Invention

The invention relates to a process for recycling specific materials fromsolid waste. More particularly, the invention relates to a process forrecovering foamed polystyrene waste from fast food restaurant trash.

2. Background of the Invention

Polystyrene is a plastic material having many uses and is particularlyuseful, when in a foam form, as a material for making food containers.It is a significant constituent of municipal solid waste and isparticularly prevalent in waste from fast food restaurants, cafeteriasand similar food service establishments. Such establishments commonlyuse trays. containers and cups made of polystyrene foam (PSF).

Fast food restaurant and cafeteria waste in addition to containing largeamounts of PSF also commonly comprises a large proportion of paperproducts (such as bags, cups and napkins), wax-coated paper products,condiment containers, plastic eating utensils and food morsels.

Recycled polystyrene foam can be used to manufacture a wide variety ofproducts such as plant pots, plastic desk organizers, foam constructioninsulation etc. and is therefore, a valuable product. Further,polystyrene foam, like most plastic, takes a very long time to degradewhen placed in landfills. Therefore, it is desirable to recyclepolystyrene foam to reduce the amount of such plastic in municipallandfills.

Various apparatus exist for separating recyclable materials frommunicipal solid waste. One such example is the process disclosed in U.S.Pat. No. 3,848,813 issued to the United States of America for aContinuous Process For Mechanically Separating Materials Contained InUrban Refuse. Most of the prior art in the area of recovering recyclablewaste relates to the recovery of glass, metals and paper from municipalsolid waste. It has previously been considered unfeasable tomechanically separate PSF waste from municipal solid waste for recyclingpurposes. The applicants are unaware of any prior art relating to therecovery of PSF from municipal solid waste or fast food restaurantwaste.

Therefore, it is an object of the present invention to provide a methodand apparatus for recycling polystyrene foam from municipal solid wasteand/or fast food restaurant waste.

It is a further object of the present invention to provide a method andapparatus for recovering polystyrene foam and paper pulp from municipalsolid waste.

It is another object of a present invention to provide a method andapparatus for recovering polystyrene foam from waste and turning theremaining waste into pelletized refuse derived fuel.

It is yet a further object of the present invention to provide a methodand apparatus for recycling waste particles having a specifiedfluidization velocity.

SUMMARY OF THE INVENTION

The invention comprises a method and apparatus for recoveringpolystyrene foam from a stream of solid waste derived from a variety ofsources, but in particular from fast food restaurant and cafeteriawaste. The method and apparatus disclosed herein, however, is highlyadaptable for recycling of other materials. The sequence of steps,arrangement of apparatus and adaptation of the method and apparatus forvarious types of waste is highly dependent on the overall contents ofthe solid waste as well as the material which is to be separated andrecycled. In addition, entire steps can be eliminated from the processdepending on the condition and contents of the waste. For instance,certain types of waste may be introduced into the process at anintermediate step while other types of waste which require additionalseparation steps may be introduced at the first stage. Therefore, analmost infinite number of adaptations of the present invention arepossible depending on the contents of the waste. The discussion below isdirected towards a method and apparatus for recycling PSF from fast foodrestaurant waste. However, various modifications and adaptations shouldbecome obvious to a person of skill in the related arts.

Waste is delivered to the apparatus primarily in plastic garbage bags.If the waste is from a fast food restaurant, the plastic bags largelycontain PSF containers, paper products, plastic eating utensils andfood. The present invention comprises two process lines. The primaryline recovers polystyrene foam (PSF) from the stream of waste. Thesecondary line converts the remaining waste to densified refusederived-fuel (d-rdf).

According to the present invention, the plastic bags are introducedcontinuously into a flail mill. The flail mill comprises a chamberhaving rotating hammers therein for tearing open the bags, liberatingthe waste within the bags, and reducing the waste particle size to apreferred range.

The waste is continuously delivered from the output of the flail mill toa rotating cylindrical trommel screen. Smaller particles of waste passthrough the screen into an undersized waste receiving area, while thelarger waste passes through the trommel onto the next stage. The bulk ofthe PSF will pass through to the trommel output without falling throughthe screen. At the output of the trommel, plastic liners are manuallyremoved from the stream of waste.

The waste is then continuously fed into an air classifier. In apreferred embodiment, the air classifier is a large rotating cylinderwhich uses an air stream to carry lighter materials, such as napkins andPSF through the cylinder, while the heavier waste, primarily wax coatedcontainers and remaining food, drops out of one end of the classifierand is removed from the primary stream of waste. The light fractionoutput of the air classifier, which comprises primarily PSF and paper,is fed into a plenum chamber where the air velocity is reduced allowingthe light fraction waste to settle to the bottom of the chamber.

The light fraction waste is then continuously delivered to a reversibleconveyor which can bring the waste either to a batch pulper or acontinuous pulper. Either of the pulpers essentially mixes the wastewith water and vigorously agitates the mixture so as to break down thepaper waste to paper pulp. The water and paper pulp is then separatedfrom the PSF by passing the mixture through a screen which allows thewater and paper pulp to pass through but retains the larger PSF wasteparticles. The PSF is air conveyed from the screen to a granulator. Theparticle size is further reduced in the granulator. The PSF is thendried and prepared for shipment.

The paper pulp and water which passes through the screen is pumped to astatic sieve where the water and paper are partially separated. Thewater is then recovered and recycled back into the apparatus. The paperpulp is further fed through a de-watering screw where addition 1 wateris removed and recycled. The de-watered paper pulp is then collected incontainers and can be sold for recycling.

The undersized waste removed in the rotating trommel and the "heavy"waste removed in the air classifier is combined and delivered to ashredder where the size of the waste is further reduced. The output ofthe shredder is sent to a pellet mill, which compresses the waste andextrudes it into small pellets. To ensure that the pellets do notreadily crumble, they are air cooled in a pellet cooler before storage.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a pictorial diagram showing the primary line of the presentapparatus.

FIG. 2 is a pictorial diagram showing the secondary line of the presentinvention.

FIG. 3 is a simplified diagram of the flail mill of the presentinvention.

FIG. 4 is a diagram of the rotary trommel of the present invention.

FIG. 5 is a diagram of the air classification assembly of the presentinvention.

FIG. 6 is a diagram of the batch pulper of the present invention.

FIG. 7 is a diagram of the continuous pulper of the present invention.

FIG. 8 is a diagram showing a schematic of the water recycling portionof the present invention.

FIG. 9 is a pictorial diagram showing the dryer of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described in detail with respect to apreferred embodiment in which it is adapted for recycling polystryenefoam from restaurant waste. It should be understood that the inventioncan be used on any type of solid waste and is not limited to recoveringpolystyrene foam. For instance, the present invention can be adapted torecover any material having a fluidization velocity (as explained below)which distinguishes it from other waste with which it is mixed. Forexample, the present invention can readily be adapted to recover filmplastic such as polyethylene and polyvinylchloride.

FIG. 1 shows a diagram of the primary line of the PSF recycling processof the present invention. This particular embodiment is adapted toaccept waste delivered to the recycling site in plastic garbage bagsfrom fast food restaurants. In this embodiment, non-processable wastesuch as large metal objects are removed from the waste prior toprocessing. A front end loader (not shown) lifts the bags of waste ontoconveyor belt 12. Conveyor belt 12 delivers a continuous stream of wastefilled plastic garbage bags to flail mill 14.

Flail mill 14 is illustrated in greater detail in FIG. 3. Such millstypically comprise a chamber 16 which is open at the top and a series ofplates 20, each having a plurality of radially projecting hammers 18extending therefrom. The plates in turn are mounted on a common shaft 21which is suitably powered for rapid rotation. The hammers 18 arepivotally secured to the plates by pivots 23. In operation, the plasticbags drop off the end of conveyor 12 into the top of the chamber 16. Asthe internal plates, 20 rapidly turns, the hammers are free to whip intothe incoming plastic bags in a flailing type motion. The flail milltears open the plastic liners releasing the waste within the garbagebags. The waste within the plastic bags from the cafeteria or fast foodrestaurant will typically comprise polystyrene containers and trays,condiment containers, eating utensils, paper cups, napkins, newsprint,wax cups, food and paper bags. Additionally, much of the waste will befurther contained within paper bags which are in the plastic garbagebags. The hammers in the flail mill will also tear open the paper bags,thus releasing the waste therewithin. In addition to tearing open theplastic garbage bags and paper bags, flail mill 14 will tend to also cutthe waste into a smaller size. Various types of flail mills arecommercially available.

The waste is discharged from the bottom of the flail mill 14 onto secondconveyor belt 22. The waste stream is carried up conveyor 22 and droppedoff the end into rotary trommel 24. Rotary trommel 24 is illustrated inFIG. 4. It comprises a cylindrical screen 26 which is rotated at apreset speed by a conventional drive such as a motor. In the preferredembodiment, the holes in the screen are 2"×4" inches. This size allowsundersized materials, such as straws, utensils, food, and condimentcontainers to fall through the screen openings while PSF, napkins andother larger waste remains within the trommel 24. Different mesh sizescan be used depending on the nature of the waste and the material whichit is wished to recover.

The input end 28 of the trommel 24 is elevated in relation to the outputend 30 so that, as the trommel rotates, the force of gravity willadvance the larger waste through the trommel and out of the output end30. The smaller waste will fall through the screen onto conveyor 26which will carry it toward the secondary line for processing as will bediscussed shortly. The trommel 24 is rotated by a motor and chain drivemounted near the input end 28 of the trommel (not shown). In normaloperation, the output of the trommel contains a high concentration ofpolystyrene foam. The undersized waste will include some amount ofpolystyrene foam, but typically in a relatively small proportion.

The waste output from output end 30 of the trommel drops onto conveyor32 which carries it to air classification assembly 34. Airclassification assembly 34 is illustrated in greater detail in FIG. 5.The air classification assembly 34 includes a rotary air classifier 36which is essentially a rotating air chamber 35 with baffles 38 disposedon the inner surface of the chamber. The chamber 35 is suitablysupported in journals or the like (not shown) for rapid rotation by asuitable and conventional drive. The drive may comprise a motor andsuitable gear train. In a preferred embodiment, the rotary airclassifier 36 is aligned at approximately a 12° angle from thehorizontal with the input end 38 lower than the output end 40. Air iscaused to flow from input end 38 to output end 40 in the chamber 35 by ablower fan (not shown). The air velocity in chamber 35 is chosen so asto be able to pick up and carry the polystyrene foam in the air streamfrom the input end 38 to the output end 40 while being unable to carryother materials such as wax coated cups and food. Any air velocity whichwould carry the polystyrene foam would also carry napkins and otherpaper products into the air stream.

Whether a waste particle is carried by the air stream or not isdetermined by the fluidization velocity of the particle. As explained ingreater detail below, the fluidization velocity of a particle is thevelocity of air required to lift the particle. Waste particles having afluidization velocity (FV) less than the air velocity in chamber 35 willbe picked up into the air stream and carried to the output end 40. Wasteparticles having a fluidization velocity greater than the air velocityin chamber 35 will not be picked up by the air stream. Fluidizationvelocity is defined as: ##EQU1##

It can be seen from the above equation that the fluidization velocity ofa waste particle depends on the mass, drag coefficient, andcross-section of the particle. It should be clear from the aboveequation that less dense particles generally are more likely to becarried by the air stream than more dense particles. However, as theequation illustrates, the fluidization velocity of a particle dependsmore accurately on the ratio of its mass to its cross-section and dragcoefficient. In any event, those waste particles which would be pickedup in the air stream in the rotary air classifier will hereinafter bereferred to as low fluidization velocity particles (low FV) since theyhave a fluidization velocity less than the air velocity in chamber 35and those waste particles which would not be picked up into the airstream in the rotary air classifier will hereinafter be referred to ashigh fluidization velocity particles (high FV) since they have afluidization velocity equal to or greater than the air velocity inchamber 35.

As the rotary air classifier 36 is rotated, the baffles 39 tumble thewaste exposing it to the air stream. In FIG. 5, the baffles are shownaligned perpendicular to the axis of the rotary air classifier. Itshould be understood that they may also be aligned parallel thereto.

The low FV particles such as polystyrene foam and napkins are lifted bythe air stream and carried towards the output end 40. The high FVparticles will remain in the chamber. Due to the slight incline of theair classifier 36 and the tumbling action of the lifters 38, gravitywill cause the high FV particles to travel backwards towards the inputend 38 and eventually drop from the rotary air classifier 36 ontoconveyor 42, shown in FIG. 2.

The PSF rich stream of waste that exits output end 40 of the rotary airclassifier 36 enters a plenum chamber 41 having a larger cross-sectionthan the rotary air classifier 36. The velocity of the air stream isreduced in the plenum chamber 41 because of the increased cross-section,thereby causing the carried material (mostly polystyrene foam andnapkins) to drop to the bottom of the plenum chamber. The bottom of theplenum chamber opens out onto conveyor belt 46.

The air assembly 34, including rotary air classifier 36 and plenumchamber 41, must be relatively airtight such that little or no air islost from the fan through the air classifier 36, plenum chamber 41 and,optionally, a bag house for removing dust particles from the air priorto discharge into the atmosphere. On the other hand, the assembly cannotbe entirely airtight since waste must enter and exit the air assembly34. Air lock 47 allows conveyor 46 to transport waste from the airassembly while still maintaining a relatively airtight seal. Air lock 47comprises a housing 49 which surrounds the conveyor belt 46 from theplenum chamber 41 to paddle wheel 51. This paddle wheel 51 forms an airlock to minimize the amount of air escaping through the housing 49.Paddle wheel 51 operates similarly to a revolving door. Paddle wheel 51is fixed on a powered axis which is driven by suitable drive means torotate at a specified speed such that the individual paddles, such aspaddle 51A come into very close proximity with the conveyor belt 46. Aswaste travels along conveyor belt 46, it passes through paddle wheel 51with a minimum loss of air. Alternately, paddle wheel 51 may be freelyrotating such that it will rotate when a waste particle contacts thelowest paddle 51A. Further, the paddles of wheel 51 may actually contactconveyor belt 46 to provide an even better seal and to allow theconveyor belt to indirectly drive the paddle wheel to rotate.

Conveyor belt 46 continuously transports the stream of waste to areversible conveyor belt 48. The reversible conveyor belt 48 can be setto deliver the PSF rich waste either to batch pulper 50 or continuouspulper 60 depending on its direction of motion. The waste remaining atthis point, which is delivered to the pulpers, almost exclusivelycomprises paper and PSF. Either pulper mixes the PSF and paper withwater and further reduces the size of the PSF particles to approximately1/2"-1".

Referring now to FIG. 6, the batch pulper 50 is shown in greater detail.The batch pulper comprises a chamber 52, having an open top 54. Thepolystyrene rich waste from conveyor 48 is dumped into the top opening54 of the chamber 52. After a specified amount of waste is dumped intothe chamber, conveyor 48 is stopped. The batch pulper operates similarlyto a household blender. After the waste is delivered to the batch pulperand the conveyor is stopped, water is added through pipe 56 and valve58. Alternately, water may be added concurrently with the delivery ofthe waste. An agitator 51 is positioned at the bottom of the tank and isactivated so as to agitate the water and waste mixture. The agitator 51comprises a blade mounted on a shaft for rotating within the pulper 50.The shaft is suitably rotated by a motor. The agitator is designed tofiberize the paper into paper pulp and reduce the size of the PSFparticles to approximately 1/2"-1". After a specified amount of time,the agitator is deactivated and the valve 53 is opened to allow thewater/paper pulp/polystyrene mixture (hereinafter slurry) to bedelivered through pipe 55 and on to further processing.

Referring now to FIG. 7, the continuous pulper 60 is shown in greaterdetail. Continuous pulper 60 comprises a chamber 61 having an opening 62at the top into which waste from conveyor 48 is dropped when theconveyor is set to deliver waste to the continuous pulper 60. Thecontinuous pulper 60 is different from the batch pulper 50 in that it isdesigned to produce a slurry of paper pulp, water and polystyrene in acontinuous stream. In normal operation, the tank is filled with slurry.Water is continuously fed into the pulper via valve 63 and pipe 64 whilewaste is continuously delivered from conveyor 48. At one side of thecontinuous pulper 60 is a powerful agitator 65. The agitator is incontinuous operation and creates a vortex which pulls the slurry intoits spinning blades. Agitator 65 shreds the polystyrene foam intoparticles of approximately 1/2"-1" in size and also fiberizes the paper.At the opposite end of the tank is a screened plate 66 having a meshsized to permit passage of particles having dimension which are lessthan set forth above. A second agitator 67 acts as a shear-shredderknife and also assures that the face of the screen 66 remains free ofmaterial so as to allow a continuous flow of slurry to exit the chamber61 via pipe 68. This second agitator 67 is positioned at the inlet sideof screen 66 with its blades close to the screen. It is suitably drivenby means not shown.

Referring now to FIG. 8, the slurry outflow from batch pulper 52 throughpipe 55 and from continuous pulper 60 through pipe 68 are both pumpedthrough pipe 70 to a vibrating screen 72. The vibrating screen 72 washesand de-waters the polystyrene product. The mesh size of the screen ischosen to retain the 1/2" to 1" polystyrene particles while allowing thewater and paper pulp to pass through. In a preferred embodiment, themesh size of the vibrating screen is on the order of 1/8"-1/4". Anoptional high pressure water spray may be added above the screen toclean and rinse the polystyrene foam and force the paper pulp throughthe screen.

The collected PSF particles on the screen are then air conveyed by ablower 81 to granulator 74 for further processing. The granulator 74 isa device that further reduces the maximum dimension of the polystyreneparticles to less than a quarter of an inch by the action of rotatingknives within a cylindrical chamber. The General Purpose 84-seriesgranulator offered for sale by Cumberland Inc. is an example of asuitable granulator.

The polystyrene foam may now be passed through a dryer 83 for finalmoisture separation. Various apparatus for drying plastic particles arecommercially available. One such device is shown in FIG. 9 and comprisesa vertically aligned cylindrical chamber 91 having an input feed 92 atthe bottom and an output discharge 93 at the top. Within the cylindricalchamber is a central shaft 94 coupled to a drive means for rotating theshaft at high speeds. Attached to the shaft at various heights are aseries of paddles 95 aligned at an angle to the horizontal. The paddlesare mounted to the shaft by a series of arms 96. As the PSF particlesare introduced from the bottom of the dryer, they are forced upward byan upward airflow caused by the rapid rotation of the paddles 95. Theparticles come in contact with the rapidly rotating paddles whichessentially beat the surface water off of the PSF particles. The PSFparticles eventually are carried upward by the airflow and the beatingof the paddles to the output end of the dryer. The dried quarter inchsize polystyrene foam particles output from the dryer are the finalproduct and can be packaged and stored for shipment.

It is noted that waste which comprises primarily paper and polystyrenemay be introduced to the apparatus at conveyor 46, subsequent to theflail mill, rotary trommel and air classification assembly. Alternately,if such waste will be the only waste provided to the apparatus, theinitial stages including the flail mill, rotary trommel and airclassification assembly may be eliminated from the overall apparatus.The stages of the preferred embodiment of the invention shown in FIG. 1which are subsequent to the air classification assembly may be used notonly for separating paper from polystyrene but also for cleaning anddrying polystyrene. Thus, the present invention is not limited to theparticular embodiment disclosed in the Figures.

The present invention also provides means for recycling the undersizedwaste which is eliminated from the stream of waste by trommel 24 as wellas the high FV waste which is eliminated in the rotary air classifier36. As stated, the undersized waste from trommel 24 drops onto conveyor26 and the high FV particles eliminated from the air stream in airclassifier 36 drop onto conveyor 42. Referring to FIG. 2, undersizedwaste from conveyor 26 is further delivered to conveyor 76 and conveyor76 delivers it to conveyor 78. The undersized waste on conveyor 78, aswell as the air classifier high FV waste from conveyor 42 are bothcarried to a further conveyor 80.

Conveyor 30 transports the combined high FV waste and "undersized" wasteto a secondary mechanical shredder 82. Secondary mechanical shredder 82may be similar to flail mill 14, comprising a chamber containing aseries of rotating hammers. Secondary mechanical shredder 82, however,is designed to reduce the particle size to approximately 1/2" to 1" insize as opposed to the flail mill's 2" to 4" output particle size. Dueto the fact that the secondary mechanical shredder is to reduce thewaste particle size to approximately 1/4 the size of the flail milloutput, the secondary mechanical shredder 82 should be installed withmore hammers than the flail mill. Otherwise, the secondary mechanicalshredder 82 and the flail mill 14 can be quite similar in design. Thesecondary mechanical shredder may also be equipped with a screen fitover the output end so as to ensure proper particle size reduction.

The secondary mechanical shredder 82 discharges its output onto conveyor84 which is inclined at a very steep angle in order to save floor space.Conveyor 84 comprises a plurality of pockets for holding the wasteparticles securely during the steep incline. A "Flexowall" conveyor isone type conveyor suitable for steep inclines. The pellet mill receivesthe shredded waste, compresses it and extrudes it into small pellets.Pellet mills are well known in the prior art for creating densifiedrefuse-derived-fuel (r-rdf) from waste and will not be described indetail. The output of the pellet mill 86 is delivered to conveyor 88which further transports the pellets to pellet cooler 90. The pelletsare air cooled in pellet cooler 90 in order to ensure that the pelletsdo not readily crumble. Pellet coolers are also well known in the priorart.

The present invention may also provide for recycling of the air used inthe air classification assembly 34. The air flow through the airclassifier is provided by a centrifugal fan. The fan pulls ambient airfrom the surrounding environment through the air classifier. In additionto picking up and carrying the light fraction of the waste, the airstream also picks up dust and carries it into plenum chamber 41. Themajority of the light fraction (which comprises mostly polystyrene andpaper) settles out of the air stream in the plenum chamber 41. However,much of the dust remains in the air flow and is carried through theplenum chamber to a bag house where the air is cleaned. The bag house isa chamber containing fabric filters in the form of large bags. The airflows through the bags which filter the dust out of the airflow. Thecleaned air may be discharged to the atmosphere or may be recycled tothe air classification assembly 34.

The water used in the pulpers is also recycled and the paper pulprecovered. A schematic of water and paper pulp flow through theapparatus of the present invention after the pulpers is shown in FIG. 8.The slurry (water and paper pulp) that passes through the vibratingscreen 72 where the polystyrene is finally separated is collected andpumped by pump 73 to static sieve 75 for fiber/water separation. Thisdevice is a stationary screen having a mesh size selected to allow thewater to drain through it while retaining the paper fiber. A pipedischarges the slurry onto the surface of the screen. The screen isslanted downwardly from the point where the pipe discharges the slurryonto the surface. The water drains through the screen while the pulpremains on top. The slant of the screen and the continuous flow ofslurry onto the top of the screen constantly pushes the paper pulp ontop of the screen towards the opposite, lower end of the screen. TheHYDRASIEVE static sieves manufactured by C. E. Bauer, a division ofCombustion Engineering Inc. of Springfield, Ohio is exemplary of thetype of static sieve that may be used in the present invention. Thepartially dried paper pulp is forced off the end of the screen where itdrops into a de-watering screw where more water is removed from thepaper pulp.

The de-watering screw comprises a funnel shaped chamber having anauger-type screw rotating therein. The paper pulp drops into the funneland the rotating screw forces the paper down into the funnel therebycompressing the paper pulp against itself and between the walls of thefunnel and the chamber to squeeze water out of the pulp. The RSP 6S-Press manufactured by Rietz Manufacturing Company of Santa Rosa,Calif. is exemplary of a de-watering screw which may be used in thepresent invention.

The water recovered at the static sieve and the de-watering screw isdrained into tank 79 where it is recycled for use in the pulpers 50 and60.

Having thus described one particular embodiment of the invention,various alterations, modifications and improvements will readily occurto those skilled in the art. Such alterations, modifications andimprovements as are made obvious by this disclosure are intended to bepart of this description though not expressly stated herein, and areintended to be within the spirit and scope of the invention.Accordingly, the foregoing description is by way of example only, andnot limiting. The invention is limited only as defined in the followingclaims and equivalents thereto.

What is claimed is:
 1. A method of recovering waste particles having afluidization velocity less than a predefined fluidization velocity, saidwaste particles termed low FV particles, from a stream of waste, saidstream of waste comprising low FV waste particles mixed with other typesof waste including waste particles having a fluidization velocitygreater than said predefined fluidization velocity termed high FVparticles, said method comprising the steps of;a. reducing the waste toparticle sizes within a first range of sizes, b. subjecting the streamof waste particles to an air stream having a velocity sufficient tocarry low FV particles while high FV particles are not carried by andare thereby eliminated from the stream of waste particles, c. mixing thestream of waste particles with water, d. agitating the mixture tofiberize any paper particle waste therein contained, and e. removing thefiberized particles and water from the stream.
 2. A method as set forthin claim 1 wherein said low FV waste is a foamed plastic.
 3. A method asset forth in claim 2 wherein said foamed plastic is polystyrene foam. 4.A method as set forth in claim 3 wherein step (a) comprises the stepsofshredding said waste to reduce the waste particles size to apredefined maximum size, and passing the stream of waste particles overa screen having openings sized to remove waste particles smaller than apredefined minimum size.
 5. A method as set forth in claim 4 whereinsaid screen is formed into a cylindrical trommel and said trommelrotates as said waste particles pass through.
 6. A method as set forthin claim 1 wherein said stream of waste comprises plastic bags withinwhich waste particles are contained and wherein the step of shreddingsaid waste tears open said plastic bags and liberates waste particlescontained within said plastic bags.
 7. A method as set forth in claim 6further comprising the step of removing said plastic bags from thestream of waste directly after said shredding step.
 8. A method as setforth in claim 7 wherein waste particles which are removed from saidstream of waste in steps a and b are formed into densifiedrefuse-derived-fuel.
 9. A method as set forth in claim 8 wherein theprocess of forming said refuse derived fuel comprises the stepsof;combining the removed waste from steps a and b to form a secondarystream of waste, shredding said secondary stream of waste to producesecondary waste particles of a second predefined size range, compressingsaid secondary waste particles, extruding said compressed wasteparticles into pellets, and cooling said pellets.
 10. A method as setforth in claim 9 further comprising the step of de-watering the removedfiberized particles from step e to produce paper pulp.
 11. A method ofrecovering foamed polystyrene waste particles from a source of wasteparticles primarily comprising paper products, wax coated paper productsand foamed polystyrene, comprising the steps of;a. shredding said wasteso as to reduce the size of the particles of said waste to a firstpredefined maximum particle size and to open any bags in said wastestream, b. delivering said waste to a rotary trommel having openings ofa second specified size so as to remove waste particles which aresmaller than a second specified size from the waste stream, c.introducing said waste to an air chamber having an air flow velocitytherein that will cause waste particles having a fluidization velocitybelow a specified fluidization velocity to be carried through saidchamber by said air flow while waste particles having a higherfluidization velocity than said specified fluidization velocity are notcarried by said air flow, said fluidization velocity being higher thanthe fluidization velocity of foamed polystyrene, d. introducing thewaste which passes thorugh said chamber into a mixing vat, e. mixingsaid waste particles with water, and f. passing the mixture through ascreen of a specified mesh size that will allow water and paper pulp topass through while retaining the foamed polystyrene particles.
 12. Amethod as set forth in claim 11 further comprising the step of agitatingsaid mixture before passing it through said screen so as to facilitatethe breakdown of the paper in said mixture to paper pulp and to cleansethe foamed polystyrene.
 13. A method as set forth in claim 12 whereinsaid waste includes plastic liners and further comprising the step ofremoving said plastic liners from the stream of waste between step b andc.
 14. A method as set forth in claim 13 wherein the stream of wasteprimarily comprises paper products, plastic eating utensils, wax coatedpaper products and foamed polystyrene products.
 15. A method as setforth in claim 14 wherein waste particles which are removed from saidstream of waste in steps a and c are combined and formed into densifiedrefuse derived fuel.
 16. A method as set forth in claim 15 furthercomprising the step of de-watering the removed paper pulp from step f.17. A method as set forth in claim 16 further comprising the stepsof;passing the water and paper pulp through a sieve to separate saidwater from said paper pulp, and recovering said water for use again instep e.
 18. An apparatus for recovering foamed polystyrene from waste,said waste comprising foamed polystyrene waste particles mixed withother types of waste particles said apparatus comprising:means forconveying a continuous stream of waste through said apparatus, means forreducing the size of said foamed polystyrene and other waste particlesto a first predetermined size range and to tear open any bags in whichwaste particles may be contained at an initial station along saidstream, means for removing from said stream of reduced particles,particles that have a higher fluidization velocity than a specifiedfluidization velocity, means for mixing said waste with water tofiberize any paper remaining in said waste stream after removal of saidhigh fluidization velocity particles, and means for separating saidfoamed polystyrene particles from said waste stream after fiberizationof paper in said stream.
 19. An apparatus as set forth in claim 18wherein said means for reducing comprises,means for shredding saidwaste, and means for eliminating from said waste stream waste particlessmaller than a first predefined size.
 20. An apparatus as set forth inclaim 19 wherein said means for shredding comprises a flail mill havinga chamber into which said waste is delivered, and a plurality ofrotating hammers for contacting and shredding said waste.
 21. Anapparatus as set forth in claim 20 wherein said means for eliminatingcomprises a rotating, cylindrical trommel constructed of a screen havingholes of said first predefined size.
 22. An apparatus as set forth inclaim 21 wherein said screen is vibrated.
 23. An apparatus as set forthin claim 20 wherein said means for removing high fluidization velocitywaste particles comprises an air classifier having,a cylindrical airchamber aligned on an incline and having a lower end for accepting wasteand an upper end for discharging waste, means for forcing air throughsaid chamber towards said upper end at a velocity that will carry wasteparticles having a fluidization velocity less than said specifiedfluidization velocity through said chamber yet allow waste particleshaving a higher fluidization velocity than said specified fluidizationvelocity to settle in said chamber, the incline of said chamberassisting said settled waste to fall out of said lower end of said airchamber and said specified fluidization velocity being greater than thefluidizaton velocity of said foamed polystyrene particles.
 24. Anapparatus as set forth in claim 23 wherein said air classifier furthercomprises,means for rotating said air chamber, baffles disposed on theinner wall of said chamber to contact the waste particles and exposethem to the air stream.
 25. An apparatus as set forth in claim 24wherein said air classifier further comprises a plenum chamber coupledto receive waste particles from the upper end of said air classifier,said plenum chamber having a cross-section larger than said airclassifier so as to reduce the velocity of the air to a velocity thatallows the carried waste particles to settle to the bottom of saidplenum chamber.
 26. An apparatus as set forth in claim 18 furthercomprising means for agitating said waste/water mixture before passingthrough said screen so as to assist in the fiberization of said paper.27. An apparatus as set forth in claim 18 wherein said means for mixingsaid waste with water comprises a batch pulper includinga mixingchamber, means for delivering a specified amount of waste from said airclassifier, means for introducing water into said mixing chamber, anagitator for mixing said waste and water, and means for pumping saidmixture towards said screen.
 28. An apparatus as set forth in claim 27wherein said means for delivering comprises a conveyor belt.
 29. Anapparatus as set forth in claim 18 wherein said means for mixing saidwaste with water comprises a continuous pulper including,means forcontinuously delivering said waste from said air classifier to saidmixing chamber, means for continuously delivering water to said mixingchamber, and an agitator in said chamber for shredding said waste andforcing the mixture toward said output end.
 30. An apparatus as setforth in claim 29 further comprising,means for receiving andtransporting said waste particles smaller than said first predefinedsize, means for receiving and transporting said high fluidizationvelocity waste particles, means for mixing said high fluidizationvelocity waste particles with said smaller waste, and means forpelletizing said mixed waste to produce densified refuse-derived-fuel.31. An apparatus as set forth in claim 30 wherein said means forreceiving and transporting comprise conveyor belts.
 32. An apparatus asset forth in claim 18 further comprising a sieve coupled to receive thewater and paper which passes through said means for separating saidwaste stream after fiberization, said sieve comprising a mesh of a sizesufficient to separate said water from said paper pulp, andmeans coupledto receive said water through said sieve, and means for pumping saidwater from said means to receive back into said means for mixing.
 33. Anapparatus as set forth in claim 18 wherein said means for separatingsaid waste stream after fiberization comprises a screen having a meshsize which will allow water and paper pulp to pass through and retainfoamed polystryene particles.
 34. A method of separating foam plasticwaste from a quantity of mixed waste which may include paper, waxedpaper, food, plastic utensils, bags, cups and plates comprising thesteps of;entraining said waste into a stream of waste, sequentiallytreating said waste stream at a series of stations to reduce the wastestream to particles within a predetermined range of sizes, thereafterremoving all but light weight particles including said foam plastic fromthe stream by directly blowing air through the stream by means of an aircurrent which continues to carry only the light weight particles in thestream, thereafter fiberizing the light weight particles other than thefoam plastic in a water matrix, and separating the foam plasticparticles therefrom.